Quantitative biotope mapping of the entire Bimini Islands, North Bahamas and two known lemon shark (Negaprion brevirostris) nursery grounds within the Bimini setting as a base for defining Essential Fish Habitat.

HUSSEY, N.E., TURNER, J.R. and GRUBER, S.H

Bimini sand flats

Abstract - Conservation efforts to protect the marine environment are critical as extensive uncontrolled development is planned for The Bimini Islands, North Bahamas. Neonate, juvenile and sub-adult lemon sharks (Negaprion brevirostris) are dependent on the Bimini lagoonal complex. For effective management and conservation an accurate knowledge of the early life history of resident sharks is required in order to define Essential Fish Habitat. Integrating Geographical Information Systems and remote sensing has proved to be effective in achieving this. The study aimed to map the biotopes of the entire Bimini Islands, and two lemon shark nursery grounds within the Bimini setting. Landsat 7 ETM+ imagery was used alongside extensive groundtruthing to obtain data on the assemblage of conspicuous species, environmental parameters, biological zones and substrata. Data was standardized and statistically analysed to define biotopes which reflected the varying density of the dominant turtle grass (Thalassia testudinum) and environmental characteristics of the three main lagoons: (1) semi intertidal, North Sound Basin, part enclosed, limited tidal flushing and consequent stunted productivity; (2) Western Lagoon with restricted tidal flow; and (3) Eastern Lagoon opening out on to the Grand Bahamas Banks. The North Sound ecosystem appears most fragile with respect to environmental/ecological disturbance proposed by the resort development, which includes extensive mangrove removal and dredging. Marked effects on the survival of young lemon sharks in the North Sound caused by siltation due to unregulated dredging (pre-development) have been published.

A dense seagrass bed (T. testudinum)

Although accuracy assessment has yet to be undertaken, field observations indicate that Landsat is suitable for producing medium/coarse resolution maps. However, complex optical parameters within the water column presented problems during classification. Within the nursery grounds, boundaries may be inaccurate due to the sensor's spatial resolution. The biotope maps will enable preliminary statistical analysis of habitat, with data on prey item and juvenile shark location and abundance to identify essential nursery habitat.

†School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Anglesey, U.K.
‡Bimini Biological Field Station and University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL 33149-1098, U.S.A.

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